Sunday, April 1, 2012

Emotion's Double-Edged Sword: When We Remember the Forest for the Trees or Not

You are driving to work when a car
suddenly crosses into your lane, careens toward your car, and
narrowly misses you, slamming into a wall instead. Your heart is
racing, and you will surely remember this incident for a while, but
will you remember anything else happening at the time? Will you
remember the song playing on the radio or other cars that were
nearby? Talks today at the CNS meeting in Chicago explored some of
the latest research seeking to understand how such emotional events
affect our memory.

In general, emotional arousal enhances
our memory of positive or negative information. Sometimes, however,
emotional arousal can help, while other times it can hinder memory of
neutral information processed before, during, or after the emotional
arousal. Mara Mather of the University of California discussed a
method she and her research team have developed to better understand
and predict when emotional arousal will enhance or impair memory of
such neutral items.

In the “arousal-based competition”
model, when multiple stimuli are present, they compete for neural
representation, Mather explained. Changing how we are introduced to
the neutral items or how we perceive their importance will determine
how well we remember them.

For example, in one study, Mather's
team showed people an image with several letters of the alphabet, a
few of which were high contrast against the background while the rest
had less contrast – to give greater salience to the high-contrast
letters. They then blasted people with either a negative stimuli –
the sound of bees buzzing – or a neutral one – cows mooing, to
see which letters people would recall best. The negative sound
enhanced short-term recall of the high contrast letters and impaired
contrast for the low-contrast letters, relative to the neutral sound.

This is one example, Mather said, of
how the arousal-based competition method favors high-priority
information – in this case the high-contrast letters. Similarly,
researchers can manipulate recall of neutral items by instructing
subjects to specifically remember the item – thereby conferring
high priority in processing that information.

Elizabeth Kensinger followed Mather's
talk by discussing the possible neural mechanisms that control when
we remember an item versus the context. Her team has done a series of
experiments that involve placing a negative (e.g. dead cat), neutral
(e.g. tumbleweed), or positive (e.g. hot-air balloon) image on a
neutral background (open prairie). They wanted to map not only
whether people remembered the items or the background but also which
brain regions were activated when they first viewed the images, so
they put people in MRI scanners while looking at different images for
short (5 seconds) time period and then tested their recall.

The researchers found that activity in
the amygdala and orbitofrontal cortex corresponded well with good
memory for items but not backgrounds, while activity in areas of the
brain associated with visual processing and attention led to
forgetting the background. Generally, high emotional arousal from
either positive or negative stimuli leads to a tradeoff between
whether we remember an item or the background. The activity within an
emotional memory region of the brain, she stressed, leads to
selective memory benefits, not enhancement for all details.

There are some exceptions to this rule,
Kensinger said, particularly in high-stress situations. There are
also some individual differences in emotional processing of memories.
For example, she found that those better at exerting control over
their actions are less likely to show tradeoffs based on stimulus –
such people can remember neutral backgrounds better but nothing can
change the enhancement of memory for high-arousal items.

Rounding out the talks were interesting
perspectives from Florin Dolcos, of the University of Illinois at
Urbana-Champaign, on how emotional distraction can both impair
working memory (e.g. make it harder to talk on a cell phone when a
car is crashing nearby) and enhance longer-term memory of the event
itself, as well as from Guillen Fernandez of Radboud University
Nijmegen on neural processes underlying how we respond to stress.
Taken together, the talks provided a robust perspective on the state
of understanding how emotions can either enhance or inhibit
attention, perception, and memory – as Dolcos said, the
“double-edge sword” of emotion and cognition. All the speakers
addressed how their work can apply to not only healthy adults but
also those with disorders such as post-traumatic stress disorder.